(1) Field of the Invention
The present invention relates generally to a pulley. More particularly, the present invention relates to a V-pulley structure which is adapted for application in a continuously variable transmission (CVT) employed in an automotive transmission system.
(2) Description of the Prior Art
In CVT systems employing a chain belt for transmitting drive power, the inside face of the pulley at which the chain belt rides is required to maintain a high coefficient of friction (.mu. value) for extended periods. (Hereinafter, the inside face of the pulley will be referred to as the pulley face.) In order to satisfy this requirement conventional V-pulleys have been subjected to surface roughing treatments in various manners. For example, the pulley surface can be hardened throughout by a carburizing treatment and, thereafter subjected to an abrasion treatment, followed by grinding to adjust the roughness of the surface. Alternately, the surface of the pulley can be hardened throughout and abraded, and, thereafter, subjected to a surface roughening treatment by means of a shot-peening process so as to form a predetermined surface roughness.
FIG. 1A and FIG. 1B are enlarged schematic illustrations showing the pulley face of a conventional V-pulley in contact with a chain belt. FIG. 1A shows the primary state of the pulley face provided with a rough surface by means of a mechanical treatment such as a shot-peening process. The rough surface contains many projections, "b" and recesses "c". A chain block "d" moves along this rough surface in the direction represented by the arrow in FIG. 1A, FIG. 1B shows the change of state of the pulley surface after running for a long period. As shown, the rough surface has been gradually abraded by the chain block, "d", and the projections, "b", have almost disappeared. The pulley face has, accordingly, become a smooth surface, "e", with a low coefficient of friction .mu..
Accordingly, such a V-pulley that is to be produced through a hardening treatment and a roughening treatment, be composed of a specific alloy material having high durability in order to maintain the pulley face with a high .mu. for a long period. Such alloy material is generally expensive. The alternative, however, would be to replace the V-pulley with a new one at short intervals in order to maintain a certain level of .mu. value.
In addition to the above problems, in order to keep the rough surface from abrading it is necessary to adequately lubricate the pulley face.